Management drives differences in nutrient dynamics in conventional and organic four-year crop rotation systems

Authors: Weyers, Sharon; Archer, David; Johnson, Jane; Wilts, Alan

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2020
Publication Date: 5/27/2020
Citation: Weyers, S.L., Archer, D.W., Johnson, J.M., Wilts, A.R. 2020. Management drives differences in nutrient dynamics in conventional and organic four-year crop rotation systems. Agronomy. 10:764. https://doi.org/10.3390/agronomy10060764.
DOI: https://doi.org/10.3390/agronomy10060764

Interpretive Summary: Researchers at the North Central Soil Conservation Research Lab in Morris, MN, and Northern Great Plains Research Laboratory in Mandan, ND, undertook a three-year evaluation of nitrogen availability in conventional and organic cropping systems. The experiment involved comparisons of mineral and organic fertilizers under a strip-tillage, four-year crop rotation. Soil mineral N was influenced by crop, and was higher in soil treatments planted to corn, and lower in soil treatments planted with wheat or alfalfa. Under organic management nitrogen mineralization increased over time and was influenced by cropping history, which was related to inputs of alfalfa and manure. However, under conventional management, N mineralization did not change, mainly because inputs of crop residues maintained a balance of carbon and N inputs. The results indicate that soil fertility is maintained by mineral N application under conventional management. Soil fertility under organic management can be improved with addition of manures and use of alfalfa in the rotation. Scientists, land managers, and policy makers will benefit from this research when they need to develop management systems for organic approaches to agriculture.

Technical Abstract: A key to developing and advancing adoption of sustainable agricultural systems is to understand how sustainable management affects N availability. Organic sources for N are potentially more sustainable. However, N must be liberated from organic sources for plants to use, which could negatively impact productivity; whereas, N from mineral fertilizers is readily available for crop uptake. Our goal was to evaluate N availability under organic (ORG) management in comparison to conventional (CNV) management to delineate dynamics influencing N availability within a strip-tilled, four-year rotation of corn (Zea mays L.)–soybean (Glycine max [L.] Merr.)–wheat+alfalfa (Triticum aestivum L./Medicago sativa L.)–alfalfa. All crops were grown each year such that each plot was established with a specific entry point (EP) into the four-year rotation as follows: EP1, corn; EP2, soybean; EP3, wheat+alfalfa; and EP4, alfalfa; this allowed for the evaluation of cropping history. The CNV management consisted of chemical weed control and pest management, and mineral fertilizers applied in full to wheat, or as starter in corn and soybean. The ORG management consisted of mechanic weed control, no pest management, and animal-based manures applied only to wheat. Soil mineral N (SMN) and cumulative net N mineralization (Nmin) were measured within all crops for three consecutive growing seasons from 2005 through 2007. Crop production, plant biomass and N content, residue inputs, and microbial biomass were also evaluated. Soil mineral N was influenced by the current crop phase and tended to be higher in treatments planted to corn, particularly in ORG, and lower in treatments planted to wheat+alfalfa or alfalfa, in both ORG and CNV. On the other hand, Nmin in the ORG system increased over time and was positively influenced by cropping history, particularly for EP4, the alfalfa rotation entry point, which had two seasons each of alfalfa and corn residue inputs and one application of manure. However, Nmin did not increase in CNV management systems, despite inclusion of alfalfa or higher residue inputs. This indicated a greater dependence on mineral fertilizer application for maintaining soil fertility. In summary, the anticipated positive changes in soil health in the ORG, reflected by the processes that positively impacted N availability, were measurable after six years of management.